SPOILERS: Forest of the Dead, TSE, and The Girl in the Fireplace. (Also, Act 1 of Dr. Horrible's Sing-Along-Blog.)
I figure everyone else is gonna be too busy with the whole 'the hammer is my ....' line to think of these:
OMG I CAN DO THIS COOL LINKY THING NOW! (Btw, oh opulent, wonderful, BUSY mod, I believe 'Dr. Horrible's Sing-Along-Blog' will soon merit its own tag ...) Scratch that. Seeing as we have Buffy jokes, Angel jokes, LOTS of Firefly jokes, and soon we're gonna have Dollhouse jokes, 'Joss Whedon in any form' is probably the best bet.